The present invention relates generally to the projection of light planes used in the construction industry and, more particularly, to a method and apparatus for the projection of first and second reference light planes which can be oriented at a selectable angle relative to one another. The second reference light plane is generated from the first light plane and is calibrated to be in alignment with a projection axis extending from the center of origin of the first light plane.
Reference light planes, typically using laser light, are employed in numerous surveying and construction applications. Such light planes can be projected throughout a work site to substantially continuously monitor and/or control the vertical height of an earth working tool, such as the blade of a motorgrader, in relation to the planes. Reference light planes can be generated by rotating laser beam devices, as disclosed in U.S. Pat. Nos. 4,062,634, 4,035,084 and 4,031,629, by a reflecting cone, as disclosed in U.S. Pat. Nos. 3,820,903 and 4,679,937 or by other appropriate devices.
In many mobile earth working machines, it is desirable to control not only the vertical height of working tools of the machines but also the direction of movement of the machines in relation, respectively, to predefined horizontal and vertical reference light planes. While this can be done by providing two of the devices disclosed in the above noted patents, preferably a pair of reference planes can be provided from a single light or laser source. For example, two orthogonal reference light planes are generated from a single laser source by the devices disclosed in U.S. Pat. Nos. 3,813,171 and 4,836,669. Such orthogonal reference light planes are indeed useful in many applications such as laying out a reference grid and other survey and control applications.
Oftentimes it is also desirable to be able to tilt the "horizontal" reference light plane such that an earth working machine, paving machine or the like can produce a grade angle on the surface which is being worked or formed with the grade angle being equal to the tilt of the horizontal plane. However, the vertical reference light plane should be maintained in a true vertical orientation regardless of any tilt of the horizontal light plane to best permit the monitoring and control functions which are performed relative to the vertical light plane. While it is common to construct reference light plane generators such that they can be tilted to correspond to desired grade angles, unfortunately, known devices for generating pairs of reference light planes from a single light or laser source are limited to generating planes which are oriented at fixed angles, usually substantially orthogonal, relative to one another or in any event, the angular orientation of the pairs of light planes is not readily adjustable.
Accordingly, there is a need for a reference light plane projector for generating two reference light planes which can be oriented at a selectable angle relative to one another. Preferably, the projector includes a calibration arrangement such that one of the reference planes o light can be calibrated to be in alignment with a projection axis extending from the center of origin of the other reference plane.